Alveolar type 2 cells marker gene SFTPC inhibits Epithelial-to-Mesenchymal Transition by upregulating SOX7 and suppressing WNT/beta-catenin pathway in non-small cell lung cancer(RNA-Seq)

Introduction: Surfactant Protein C gene (SFTPC) is a marker gene of alveolar type 2 cells (AT2), which are the key structures of alveoli. Mutations or deletions in SFTPC cause idiopathic pulmonary fibrosis (IPF). Importantly, IPF is an independent risk factor for non-small cell lung cancer (NSCLC). It suggests that abnormal expression of SFTPC may be relevant to development of NSCLC. However, the function and mechanism of SFTPC in NSCLC are still poor understood until now.Methods: The expression of SFTPC and the relationship between SFTPC and prognosis of NSCLC were analyzed in TCGA database and our collected clinical NSCLC tissues. Subsequently, the function and mechanism of SFTPC in NSCLC were explored by RNA-sequence, qRT-PCR, Western blot, Immunohistochemical, Wound-healing, Millicell, Transwell assays and mouse tumor xenograft model.Results: SFTPC was dramatically downregulated in NSCLC tissues from TCGA database and 40 out of 46 collected clinical LUAD tissues compared with adjacent non-tumor tissues. Low expression of SFTPC was associated with poor prognosis of LUAD by TCGA database. Importantly, we confirmed that overexpression of SFTPC significantly inhibited Epithelial-to-Mesenchymal (EMT) Transition process of NSCLC cells by upregulating SOX7 and then inactivating WNT/beta-catenin pathway in vitro and in vivo. Particularly, we discovered that low expression of SFTPC was associated with EMT process and low expression of SOX7 in NSCLC tissues.Conclusion: Our study revealed a novel mechanism of SFTPC in NSCLC development. Meanwhile, it also might provide a new clue for exploring the molecular mechanism about NSCLC development in patients with IPF in the future.

引言：表面活性蛋白C基因（SFTPC）是肺泡Ⅱ型上皮细胞（alveolar type 2 cells, AT2）的标记基因，而AT2是构成肺泡的核心功能结构。SFTPC的突变或缺失可引发特发性肺纤维化（IPF）。值得注意的是，IPF是非小细胞肺癌（NSCLC）的独立危险因素，这提示SFTPC的异常表达可能与NSCLC的发生发展相关。然而截至目前，SFTPC在NSCLC中的功能与作用机制仍未被充分阐明。
方法：本研究在癌症基因组图谱（TCGA）数据库及本课题组收集的临床NSCLC组织中，分析了SFTPC的表达水平及其与NSCLC患者预后的关联。随后，本研究通过RNA测序、实时荧光定量聚合酶链反应（qRT-PCR）、蛋白质印迹（Western blot）、免疫组化、划痕愈合实验、Millicell小室实验、Transwell实验以及小鼠肿瘤异种移植模型，对SFTPC在NSCLC中的功能与作用机制进行了探究。
结果：与癌旁正常组织相比，TCGA数据库中的NSCLC组织及本课题组收集的46例肺腺癌（LUAD）临床组织中的40例，均呈现出SFTPC的显著下调。基于TCGA数据库的分析显示，SFTPC低表达与LUAD患者的不良预后显著相关。重要的是，本研究证实，在体内外实验中，SFTPC过表达可通过上调SOX7的表达并进而失活WNT/β-连环蛋白通路，显著抑制NSCLC细胞的上皮间质转化（Epithelial-to-Mesenchymal Transition, EMT）过程。尤为关键的是，本研究发现NSCLC组织中SFTPC低表达与EMT进程及SOX7低表达密切相关。
结论：本研究揭示了SFTPC在NSCLC发生发展中的全新作用机制，同时也为未来探索IPF患者合并NSCLC的发病分子机制提供了新的研究方向。